The present invention relates generally to systems and methods for the recovery of subterranean resources and, more particularly, to a cavity well positioning system and method.
Subterranean deposits of coal contain substantial quantities of entrained methane gas limited in production in use of methane gas from coal deposits has occurred for many years. Substantial obstacles, however, have frustrated more extensive development and use of methane gas deposits in coal seams. The foremost problem in producing methane gas from coal seams is that while coal seams may extend over large areas of up to several thousand acres, the coal seams are fairly shallow in depth, varying from a few inches to several meters. Thus, while the coal seams are often relatively near the surface, vertical wells drilled into the coal deposits for obtaining methane gas can only drain a fairly small radius around the coal deposits. Further, coal deposits are not amenable to pressure fracturing and other methods often used for increasing methane gas production from rock formations. As a result, once the gas easily drained from a vertical well bore in a coal seam is produced, further production is limited in volume. Additionally, coal seams are often associated with subterranean water, which must be drained from the coal seam in order to produce the methane.
Horizontal drilling patterns have been tried in order to extend the amount of coal seams exposed to a drill bore for gas extraction. Such horizontal drilling techniques, however, require the use of a radiused well bore which presents difficulties in removing the entrained water from the coal seam. The most efficient method for pumping water from a subterranean well, a sucker rod pump, does not work well in horizontal or radiused bores.
A further problem for surface production of gas from coal seams is the difficulty presented by under balanced drilling conditions caused by the porousness of the coal seam. During both vertical and horizontal surface drilling operations, drilling fluid is used to remove cuttings from the well bore to the surface. The drilling fluid exerts a hydrostatic pressure on the formation which, if it exceeds the hydrostatic pressure of the formation, can result in a loss of drilling fluid into the formation. This results in entrainment of drilling finds in the formation, which tends to plug the pores, cracks, and fractures that are needed to produce the gas.
As a result of these difficulties in surface production of methane gas from coal deposits, the methane gas which must be removed from a coal seam prior to mining, has been removed from coal seams through the use of subterranean methods. While the use of subterranean methods allows water to be easily removed from a coal seam and eliminates under balanced drilling conditions, they can only access a limited amount of the coal seams exposed by current mining operations. Where longwall mining is practiced, for example, underground drilling rigs are used to drill horizontal holes from a panel currently being mined into an adjacent panel that will later be mined. The limitations of underground rigs limits the reach of such horizontal holes and thus the area that can be effectively drained. In addition, the degasification of a next panel during mining of a current panel limits the time for degasification. As a result, many horizontal bores must be drilled to remove the gas in a limited period of time. Furthermore, in conditions of high gas content or migration of gas through a coal seam, mining may need to be halted or delayed until a next panel can be adequately degasified. These production delays add to the expense associated with degasifying a coal seam.
Additionally, precisely locating and securing downhole equipment, such as pumping units for removing water from the coal seam in order to produce the methane, in a well bore is difficult. For example, various alignment tools are generally used to locate the equipment at a desired location and locking mechanisms are actuated to secure the equipment at the desired location. The locking mechanisms must then be unlocked to accommodate retrieval of the equipment from the well bore. Malfunctions of the alignment tools and locking mechanisms results in delay and, oftentimes, repeated mining procedures.
The present invention provides a cavity well positioning system and method for positioning down-hole pumps and equipment within a subterranean cavity that substantially eliminates or reduces the disadvantages and problems associated with previous systems and methods. In particular, the present invention provides a cavity well positioning system and method for efficiently positioning and removing down-hole equipment from within a subterranean cavity 20 without requiring additional locking, unlocking or alignment tools to facilitate the positioning and withdrawal of down-hole equipment.
In accordance with one embodiment of the present invention, a subterranean cavity positioning system includes a down-hole device and a cavity positioning device rotatably coupled to a well portion of the down-hole device. The cavity positioning device includes a counterbalance portion operable to automatically rotate the cavity positioning device from a retracted position to an extended position as the cavity positioning device transitions from a well bore into the subterranean cavity. The counterbalance portion is also operable to align the cavity positioning device with the well bore as the down-hole device is withdrawn from the subterranean cavity.
According to another embodiment of the present invention, a method for automatically positioning and retrieving down-hole equipment in a subterranean cavity includes providing a cavity positioning device coupled to a well bore portion of a down-hole device and deploying the down-hole device and the cavity positioning device into a well bore. The cavity positioning device is disposed in a retracted position relative to the well bore. The method also includes running the down-hole device and the cavity positioning device downwardly within the well bore to the cavity. The cavity positioning device automatically transitions to an extended position relative to the well bore in the cavity. The method further includes positioning the down-hole device at a predefined location in the cavity by contacting a portion of the cavity with the cavity positioning device.
Technical advantages of the present invention include providing a positioning system for automatically positioning down-hole pumps and other equipment in a cavity. In particular, a rotatable cavity positioning device is configured to retract for transport in a well bore and to extend within a down-hole cavity to optimally position the equipment within the cavity. This allows down-hole equipment to be easily positioned and secured within the cavity.
Other technical advantages of the present invention will be readily apparent to one skilled in the art from the following figures, description, and claims.